The present invention is directed to imaging recorders and more particularly to an imaging recorder device wherein images are produced by the application of heat patterns to a thermal imaging material.
The employment of a thermal imaging medium to provide stable images of high quality is known to have a potentially wide range of applications, and various devices providing for the application of heat to such imaging materials have been proposed. One source of heat which has now become somewhat conventional for exposing thermal imaging media are lasers chosen of sufficient power output, and appropriately modulated while scanning a medium in an image pattern. One advantage to the employment of such laser devices is that the time required for irradiating the imaging material in this manner is relatively short in comparison with other heat sources such as Xenon flash tubes.
A typical thermal imaging medium employing laser diodes for irradiation is disclosed in International Application PCT/US87/03249.
In applying the image upon a medium disclosed in the aforementioned application, the diodes are conventionally mounted such that the light radiating elements are linearly arranged in a direction perpendicular to the path of movement of the material and an optical means is disposed between the light radiating elements and the path of the material for converting the image of the light radiating elements on the material to an irradiated region which is elongated in a direction perpendicular to the movement of the medium, or in the instance where the medium is mounted on a drum, in the axial direction of the drum.
In this prior arrangement, each of the adjacent elements of the linear laser array exposes corresponding adjacent traces on the imaging medium as it is moved past the focused lasers producing the spot on the imaging medium.
If each of the laser elements in the writing spot is more powerful than the medium exposure threshold, then the medium is exposed over the entire spot during the imaging process.
While the above-described laser scanning configuration is successful in producing satisfactory images on the imaging medium, a problem exists when the power output of the laser elements differ. In order completely to expose the medium, the laser power of all the elements must be increased so that the weakest element is above the medium exposure threshold. In the best case, the weakest element is typically half the average element power and therefore the average element power needs to be twice the medium threshold power in order to insure proper exposure by the weakest element. The result of this is generally a waste of half the total laser power.
In another instance, one or two elements may burn out, even though the total laser power is correct. In this case, increasing the total laser power will not expose all the tracks of the medium and the printer will fail to print acceptable images. Element burn out is a common problem and laser manufacturers often will not specify the number of emitting elements but the total diode output instead.
In view of the above, an object of the present invention is to provide an imaging recorder employing a plurality of light radiating elements which is effective to minimize the power requirements to operate the recorder.
Another object of the invention is to provide an imaging recorder employing a plurality of light radiating elements which is effective to produce acceptable images should one or more of the elements fail to operate.
A further object of the invention is to provide an imaging recorder employing a plurality of light radiating elements wherein the above objectives are achieved employing a structure which is simple in construction and economically produced.